Mixed sodium-calcium roller bearing grease



April 29, 1958 R. F. NELSON 2,832,738

' MIXED somma-CALCIUM ROLLER BEARING GREASE Filed Sept. 8, 1955 United States Patent O MIXED SDIUM-CALCIUM ROLLER BEARING GREASE Roy F. Nelson, Port Arthur, Tex., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application September 8, 1955, Serial No. 533,196

7 Claims. (Cl. 252-40) This invention relates to a high dropping point roller earing grease adapted for use in railroad lubrication. More specifically, this invention involves the formulation of a mixed sodium-calcium base grease having a dropping point meeting iield requirements.

The field requirements for a roller bearing grease have been satisfactorily met for some time by a mixed sodiumcalcium base grease of hydrogenated castor oil. This mixed base grease gave good performance and was widely used by the railroads for journal bearing lubrication.

However, when the dropping point specification for roller bearing grease was raised to a minimum of 325 F., this mixed sodium-calcium base grease consistently failed this test.

This invention involves the discovery that the dropping point deficiency of a mixed sodium-calcium base grease is eliminated by using as a soap-forming base a mixture of hydrogenated castor oil and l2-hydroxy stearic acid or its low molecular weight inonoalkyl ester in prescribed proportions. The high dropping point greases of this invention comprise an oleaginous lubricating base as the major component, a thickening agent lcomprising a mixed sodium-calcium salt of a soap-forming material consisting of 35 to 70 percent hydrogenated castor oil and 30 to 65 percent 12-hydroxy stearic acid or its lower alkyl monoester.

Replacement of a portion of the glycerideA with l2-hydroxy fatty acid and the resulting reduction of the glycerine content of the grease composition has a three-fold effect. As will be shown later, the increase in dropping point is a direct function of the increase of the quantity of 12-hydroxy stearic acid in the soap-forming component. When the l2-hydroxy stearic acid content is above the prescribed minimum of 30 percent in the soap precursor, there is no difficulty in meeting the 325 F. minimum dropping point of the AAR specification. Secondly, the use of the prescribed mixture of hydrogenated castor oil and 12-hydroxy stearic acid resulted in improved yields of mixed sodium-calcium base grease. This increase in yield is not obtained when l2-hydroxy stearic acid constitutes more than 65% of the soap-forming component. Thirdly, shear stability, which is a complex function, is also affected by the acid-glyceride ratio. Apparently, optimum results from the standpoint of shear stability are obtained with a high acid concentration, that is, in the range of 60 to 65% of the soap-forming component.

The soap-forming component of the mixed sodium-calcium base grease of this invention comprises 35 to 70 percent hydrogenated castor oil and 30 to 65 percent 12- hydroxy stearic acid or a lower alkyl monoester of 12- hydroxy stearic acid. It is necessary that the composition of soap precursor fall within the prescribed ranges in order to obtain dropping point improvement, increase in yield and the desired shear stability characteristics. has been found that optimum results from the standpoint of dropping point, yield, deposit formation and perform- 2,832,738 Patented Apr. 29, 1958 ance are obtained when the mixed sodium-calcium base soap is derived from a 50-50 or 60-40 hydrogenated castor oil-free hydroxy fatty acid mixture.

The lower alkyl monoesters which can be used in place of 12-hydroxy stearic acid in the mixed sodium-calcium base greases of this invention comprise C1 to C5 alkyl monoesters such as methy1-12-hydroxy stearate, ethyl-12- hydroxy stearate, butyl-lZ-hydroxy stearate, n-amyl-12- hydroxy stearate and isopropyl-lZ-hydroxy stearate. During saponification of the soap-forming mixture, these monoesters are converted to mixed soaps and free alcohol which distills from the grease mixture during the saponication and dehydration operations. The C1 to C5 alkyl monoesters have the same action as 12-hydroxy stearic acid in reducing the glycerine content of the mixture, and in producing high dropping point mixed sodium-calcium base roller bearing greases when used in admixture with hydrogenated castor oil as the soap-forming material in the prescribed proportions. Because of lower cost 12- hydroxy stearic acid is generally used.

The ratio of sodium soap to calcium soap required lfor high dropping points and high yields falls within the limits of 3.5:1 to 8:1. Higher calcium soap concentrations than those specified decreased both the yield and dropping point of the grease. Products having higher sodium soap contents than those prescribed in the above ratios have inferior shear stability as indicated by a tendency to harden excessively after being subjected to shear. Excellent results have been obtained with sodium to calcium soap ratios between 5.3:1 and 7.2:1.

It is necessary to control the excess alkali metal hydroxide content of the mixed sodium-calcium base grease of the invention below about 0.15 weight percent in order to obtain commercially feasible yields while maintaining the dropping point at the desired level. Since the presence of excess alkali tends to increase the dropping point of the mixed sodium-calcium base grease, it is advisable to use excess alkali concentrations between 0.01 and 0.15 and preferably 0.02 to 0.06 weight percent NaOH. It is possible to have a satisfactory grease with free fatty acid contents up to 0.1 weight percent, but such greases are obtained in poorer yield than greases having an excess alkali concentration below 0.15 weight percent.

The procedure used for formulating the greases of this invention is essentially a conventional one. The general procedure for preparing the greases is as follows:

The fat mixture, water and a portion of the oil, which is usually from about l to 1.5 times the amount of the fat, are charged to a kettle and heated to about 190 F. Lime in the form of dry powder is added and the fat is saponiied at a temperature of 190 to 210 F.; the normal period for this saponification is about 1 hour. Caustic soda solution is then added and the remaining fat saponified at 190 to 210 F.; this saponiiication requires from about Vt to 5 hours. When saponification is complete, the soap base is dehydrated by heating to a temperature less than about 320 F. and preferably between 300 and 315 F.; periods of about 2 to 8 hours are used for the dehydration. The remaining oil is then worked in and oxidation inhibitor incorporated when the temperature of the grease is between 200 and 220 F.

Since roller bearing grease for use in the railroads is a l-arge volume product and must be available at relatively low cost, the oleaginous lubricating base is a hydrocarbon mineral oil. A paraliin base, naphthene base or mixed base oil can be used but it has beenfound that -optimum performance is obtained when the oil component is a refined parailin base oil. Preferred lubricating bases are paraiiin base oils having an SUS viscosity at F. between 120 and 800 and preferably 450 to 550, which have been subjected to solvent rening and solvent dewaxing in addition to acid treating and clay contacting.

3 A blend of paraitin oils refined as outlined above and comprising approximately 1 part of a 10 grade oil having an SUS viscosity at 100 F. between 160 and 175, a V. I. of 95 minimum, a pour of 10 maximum, and 3 parts of a 40 grade oil having an SUS viscosity at 100 F. of 800 to 890, a V. I. of 85 minimum and a pour of 5 F. maximum is particularly etective and is generally used.

The iinished roller bearing grease usually contains a conventional anti-oxidant, such as diphenylamine and/ or alpha naphthylamine. The anti-oxidant concentration is between 0.1 and 1 weight percent but a concentration of 0.5 weight percent is generally used. Diphenylamine is a preferred anti-oxidant.

The critical nature of the prescribed glyceride-fatty acid mixture on the properties of the resulting mixed sodium-calcium roller bearing grease are shown in Table l wherein a series of greases were prepared in which the only significant variable was the nature of the soap precursor. The ratio of sodium to` calcium soap was held constant in this series of greases at 7.2:1 and the excess alkali metal hydroxide content was maintained at Vabout 0.1 weight percent. The soaps were linished to a controlled worked penetration at 77 F. between 355 and 370, which resulted in a difference in the soap content- `which difference is a function of fat composition on yield.

The procedure employed was that previously described and simply involved mixing of the fat mixture, water and a portion of the oil which was 1.14 times the amount of fat, saponifcation with lime followed by saponication with caustic soda at a temperature between 190 and 210 F., dehydration at a temperature below 320 and usually between 300 and 315 F. for two hours, and addition of the remainder of the oil and 0.5 weight percent diphenylamine during the stirred cooling of the grease. The oil was added until the grease had a controlled worked penetration of 355 to 370 in each product.

off and 12.8 and 15.9 percent soap are required to meet this worked penetration specication at 80% and 100% l2hydroxy stearic acid in the soap. The relationship between 12hydroxy stearic acid concentration of soap precursor and the yield is shown graphically in Fig. 2 of the accompanying drawing.

The data in Table I and Figure 2 clearly indicate that the soap concentration in the roller bearing greases of the invention usually falls between 8 and 11 percent. Soap concentrations in this range meet the field requirements of a worked penetration at 77 F. between 340 and 370. It is apparent that harder greases are prepared using soap concentrations up to 15 weight percent and that softer greases are prepared by using lower soap concentrations as low as 5 weight percent.

A high dropping point roller bearing grease having a sodium soap to calcium soap ratio of 7.2:1 and prepared from a -50 mixture of hydrogenated castor oil and l2-hydroxy'stearic acid was produced in the plant as follows:

L500 pounds of hydrogenated castor oil, 500 pounds of V l2-hydroxy stearic acid, 260 pounds of water, 1000 pounds of a 10 grade solvent refined, solvent dewaxed parain base distillate having SUS viscosities at 100 F. and 210 F. of 171.3 and 44.5, respectively, and 15.7 pounds of hydrated lime were charged to a steam-heated kettle. The reaction mixture was heated with stirring to a temperature of 190-195 F. to etect substantial saponiiication. After about 1 hour at this temperature, 255 pounds of 49% caustic solution were added. After addition of the caustic solution was completed, the reaction mixture was maintained at a temperature between 197 and 207 F. for about 3 hours, and the kettle was then slowly raised with stirring to a temperature between 303 and 315 F. `for dehydration of the reaction mixture. Dehydration was substantially complete in about 4 hours.

Table I Field Requirements Fat Ratio Used:

Hydrogenated Castor Oil 100 60 50 0 12Hydroxy Stearic Acid- 0 40 50 100 Calc. Glycerine Content of Grease, Percent. 1. 2 0. 57 0. 47 0. 0 Penetration:

Unworked, 77 F 337 308 359 340 Worked, 77 F 358 348 305 359 340-370. Worked, 77 F., Punched 0 F 204 255 238 200 Min. 100,000 Strokes- Value 368 370 377 373 390 Max. Change from Worked 10 22 12 14 25 Max. Dropping Point, F 317 330 361 380 25 Min Soap Content, Percent (Calc.) 13.2 10. 3 10.0 15. 9 Shell Roll Test:

Mcropenetration- Originally 132 13E 188 178 Too soft.-- 200 Rolled 199 204 229 210 Too soft..- 232 The data in the foregoing table shows very clearly that the dropping point of the grease appears to be a direct function of the acid-glyceride ratio. As shown in Figure 1 of the accompanying drawing, the dropping point increases as the concentration of 12-hydroxy stearic acid increases in the soap-forming component. lt is clear from Figure 1 that the presence of at least 30 weight percent 12-hydroxy stearic acid in the fat assures a dropping point well over the 325 minimum field requirement.

The data in Table I also clearly shows that when the 12-hydroxy stearic acid content of the soap-forming cornponent is in the prescribed 30 to 65 percent range, substantial improvement in yield is obtained. A Worked penetration of 345 to 375 at 77 F. requires 13.5 percent soap when the soap precursor is 100 percent glyceride, whereas the same penetration is obtained with 8.9 to 10.3 percent soap concentrations when the glyceride-hydroxy fatty acid ratio falls within the prescribed limits. It is noteworthy that when the lZ-hydroxy stearic acid concentration is above the percent limit, the yield'falls During the stirred cooling of the grease, 1146 pounds of the 10 grade distillate and 5423 pounds of a 40 grade solvent refined, solvent dewaxed paraffin base distillate having SUS viscosities at F. and 210 F. of 850 and 77.9, respectively, were added. 42 pounds of diphenylamine were added at a temperature of about 200 F. and about 0.25 pound of yellow dye dissolved in a portion of the 40 grade distillate was added at about the same temperature. The grease was drawn at about F. There was obtained 8678 pounds of finished grease having the following composition:

Diphenylarnine 0.47

essayes This product had the following properties:

Table 111 Penetration:

Unworked, 77 F 359 Worked, 77 F 349 100,000 stroke:

Value 349 Change None 0 F 251 Dropping point, F 359 Water, percent None Shell Roll Test:

Micropenetration- Original 197 Rolled 171 The foregoing example proves that a plant batch of grease having a high dropping point is prepared from a soap-forming mixture comprising 50% hydrogenated castor oil and 50% 12-hydroxy stearic acid.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A high dropping point roller bearing grease comprising an oleaginous lubricating base as the major component, a mixed sodium-calcium soap of a mixture comprising 35 to 70 percent hydrogenated castor oil and 30 to 65 percent of soap precursor selected from the group consisting of 12-hydroxy stearic acid, lower monoalkyl esters of said 12-hydroxy stearic acid and mixtures thereof, the sodium to calcium soap ratio being between 3.5 :1 and 8:1 in said mixed soap.

2. A roller bearing grease according to claim 1 in which the mixture comprises to 60% hydrogenated castor oil and 50 to 40% 12-hydroxy fatty acid.

3. A roller bearing grease according to claim 1 in which the oleaginous lubricating base is a solvent refined, solvent dewaxed parain base oil having an SUS viscosity at 100 F. in the range of 100 to 800.

4. A roller bearing grease according to claim 1 in which the oleaginous lubricating base comprises one part of 10 grade solvent refined, solvent dewaxed parain base oil and three parts of a solvent refined, solvent dewaxed 40 grade oil.

5. A roller bearing grease according to claim 1 in which the sodium to calcium soap ratios fall between 5.3:1 and 7.2:1.

6. A high dropping point roller bearing grease compricing a mineral oil lubricating base as the major component, a mixed sodium-calcium soap of a mixture comprising 35 to 70% hydrogenated castor oil and 30 to 12-hydroxy stearic acid, said mixed soap having a sodium to calcium soap ratio between 5.3:1 and 7.2:1 and an excess sodium hydroxide content less than 0.15 percent.

, 7. A roller bearing grease according to claim 6 having an excess sodium hydroxide content between'0.02 and 0.1.

References Cited in the le of this patent UNITED STATES PATENTS Morway et al Feb. 14, 1950 Ashburn et al May 23, 1950 OTHER REFERENCES 

1. A HIGH DROPPING POINT ROLLER BEARING GREASE COMPRISING AN ALEAGINOUS LUBRICATING BASE AS THE MAJOR COMPONENT, A MIXED SODIUM-CALCIUM SOAP OF A MIXTURE COMPRISING 35 TO 70 PERCENT HYDROGANATED CASTROR OIL AND 30 TO 65 PERCENT OF SAOP PRECUSTOR SELECTED FROM THE GROUP CONSISTING OF 12-HYDROXY STEARIC ACID, LOWER MONOALKYL ESTERS OF SAID 12-HYDROXY STEARIC ACID AND MIXTURES THEREOF, THE SODIUM TO CALCIUM SOAP RATIO BEING BETWEEN 35-1 AND 9:1 IN SAID MIXED SOAP. 